99 Aquarii

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99 Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of 99 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 23h 26m 02.78566s[1]
Declination –20° 38′ 31.251″[1]
Apparent magnitude (V) 4.37[2]
Spectral type K4 III[3]
U−B color index +1.815[2]
B−V color index +1.431[2]
Variable type Suspected[4]
Radial velocity (Rv) +15.7[5] km/s
Proper motion (μ) RA: –50.72[1] mas/yr
Dec.: –64.22[1] mas/yr
Parallax (π) 11.51 ± 0.21[1] mas
Distance 283 ± 5 ly
(87 ± 2 pc)
Radius 33[6] R
Surface gravity (log g) 1.66[7] cgs
Temperature 3980[7] K
Metallicity [Fe/H] –0.20[7] dex
Other designations
b02 Aquarii, BD–21 6420, HD 220704, HIP 115669, HR 8906, NSV 14554, SAO 191900.[8]

99 Aquarii is the Flamsteed designation for a star in the equatorial constellation of Aquarius. The Bayer designation for this star is b2 Aquarii. It is visible to the naked eye with an apparent visual magnitude of 4.38;[2] according to the Bortle Dark-Sky Scale this is bright enough to be seen even from city skies under ideal viewing conditions. Based upon parallax measurements, the distance to this star is around 283 light-years (87 parsecs).[1]

This is a giant star with a stellar classification of K4 III.[3] It is a suspected variable star that apparently ranges in magnitude between 4.35 and 4.45.[4] The measured angular diameter of this star is 3.55 ± 0.21 mas.[9] At the estimated distance of Delta Ophiuchi,[1] this yields a physical size of about 33 times the radius of the Sun.[6] The outer atmosphere has an effective temperature of 3980 K,[7] giving it the orange-hued glow of a cool, K-type star.[10]

This star was a candidate member of the Ursa Major Moving Group based on the work of American astronomer Nancy Roman, but this membership is now in question.[11]


  1. ^ a b c d e f g van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society 172: 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667. 
  3. ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H. 
  4. ^ a b Samus, N. N.; et al. (March 2012), "NSV 14554", General Catalog of Variable Stars, retrieved 2012-07-12. 
  5. ^ Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953QB901.W495...... 
  6. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. . The radius (R*) is given by:
    \begin{align} 2\cdot R_*
 & = \frac{(87\cdot 3.55\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
 & \approx 66\cdot R_{\bigodot}
  7. ^ a b c d McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527. 
  8. ^ "99 Aqr -- Variable Star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-07-11. 
  9. ^ Richichi, A.; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039. 
  10. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16. 
  11. ^ Chupina, N. V.; Reva, V. G.; Vereshchagin, S. V. (June 2006), "Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars", Astronomy and Astrophysics 451 (3): 909–916, Bibcode:2006A&A...451..909C, doi:10.1051/0004-6361:20054009.  See table 7.

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